The present invention relates to a magnetic card transport system for electronic typewriters and more particularly to a card transport system having prealigned components.
An electronic typewriter provides the capability of recording and storing information from the typewriter on magnetic cards. The information may later be read by the machine and used to control the operation of the machine.
Information is applied to and read from the card along discrete flux lines extending longitudinally on the surface of the card and spaced across the width of the card. The information is applied to or read from the card by the use of a magnetic head which scans the surface of the card as the card is moved back and forth under the magnetic head. The magnetic head is moved across the width of the card from one flux pattern to the adjacent flux patterns. For the magnetic head to perform a read or write function from a magnetic card, the magnetic head must be accurately set relative to the flux patterns on the card along three axes of orientation, that is with respect to the roll, pitch and skew or azimuth axes relative to the planar surface of the card. Additionally, because the card and the information stored thereon must be interchangeable from machine to machine such that information may be applied to a card by one machine and read from the card by a second machine, the flux patterns on the card must be along predetermined axes over the width of the card. Further, because of the critical nature of the relationship between the card and the magnetic head which performs both read and write functions, the mechanism for driving the card forward and back under the magnetic head must be accurately aligned relative to the transport axis along which the card is moved so as not to interfere with the relationship between the card and the magnetic head.
In prior art electronic typewriters, the critical relationship between the magnetic head and card and between the magnetic card and the drive assembly for driving the card longitudinally under the magnetic head have been accurately preset at the factory when the machine is put into operation. However, none of the prior art systems have provided an accurate and quick method for resetting the relationship between these elements once one of the components or components relating to the operation of one of these elements has been removed or altered as during replacement or repair. Heretofore, whenever the magnetic head or the structure supporting the magnetic head for movement laterally across the width of the card is removed for repair or replacement, the realignment of the magnetic head along the three axes of adjustment has required excessive time and labor. Without the advantage of having the factory fixtures and adjustment equipment in which the head is originally set, the requirement that the head be properly adjusted in roll, pitch and skew or azimuth has required substantial service time and in many cases, where sufficient care has not been taken, the setting or adjustment has not been adequate for the proper operation of the machine.
The adjustment required is critical in that the alignment of the magnetic head in skew or azimuth must generally be within nine minutes of perfect adjustment. Moreover, the sensitive surface of the magnetic head must be within thirty millionths of an inch of the upper surface of the magnetic card from which information is being read or to which information is being applied.
Additionally, the magnetic head must be settable along predetermined axes across the width of the magnetic card to correspond to the standard flux pattern locations and flux azimuth coincidence to facilitate and make possible interchangeability of cards from one machine to another. The magnetic head must generally be within two thousandths of an inch of predetermined flux pattern locations across the width of the card and nine minutes of arc azimuth in flux coincidence.
In the past, setting the magnetic head at appropriate flux pattern positions has been accomplished by the use of what is known in the trade as a CE card. With a CE card, standard flux patterns are "read" from the card and a field serviceman makes the appropriate adjustments of the magnetic head position along the transverse width of the magnetic card. This procedure, in addition to being subject to great inaccuracy either from failure to properly "read" the CE card or as a result of the use of old or damaged CE cards, is a very tedious and time consuming operation. As a result, such a technique has been completely inadequate in providing a simple and accurate method for assuring the proper adjustment of the magnetic head with relation to the magnetic card. Further, the ability to read a CE card successfully was not a guarantee of interchange capability due to possible minor but significant difference in CE cards written on different card master programmers.
Additionally, the alignment of the driving mechanism for moving the card longitudinally past the magnetic head has been strictly a mechanical adjustment requiring the serviceman to make the adjustments individually on a machine by machine basis. Because of the accuracy required for the proper operation of an electronic typewriter or similar machine using a magnetic head for reading or writing from or to a magnetic card, these mechanical adjustments have been completely unacceptable in meeting the need for a quick and accurate readjustment of the elements in the system subsequent to removal or repair of one of the elements of the system.